This invention relates to hydraulic systems, and more particularly to a hydraulic apparatus including a pressure clamped hydraulic pump.
In a hydraulic apparatus including a motor driven pump, it is often desirable to make the component parts as small and highly integrated as possible, so that the apparatus will be compact, light weight, inexpensive to manufacture and maintain, and highly reliable. U.S. Pat. No. 6,152,715 describes a pressure clamped hydraulic pump that is held together by pressure produced in the pump, thereby allowing the elimination of bolts and other fasteners used to hold together pumps of a more conventional design.
Although prior pressure clamped pumps, such as the pump of the ""715 patent, provide considerable reduction in size and complexity as compared to more conventional pump designs, further improvement is needed to resolve several problems related to using a pressure clamped pump in a hydraulic apparatus. These problems include difficulty in aligning the drive shaft of the pump with the output shaft of a drive motor, lack of provisions for positively retaining the drive shaft so that it cannot be inadvertently pulled out of the pump, and inherent restrictions on the size of the pump inlet resulting from the structure of prior pressure clamped pumps.
As shown in FIGS. 1-4, The pressure clamped pump 100 of the ""715 patent includes a housing 102 having an external threaded portion 104 that engages threads 106 in a cavity 108 of a valve block 110, and a pair of o-ring seals 112, 114 that mate with surfaces of the cavity 108 to seal the inlet and outlet of the pump 100, so that the pump 100 may be installed by simply screwing the pump 100 into the cavity 108 until the seals 112, 114 seat against the surfaces of the cavity 108.
As shown in FIG. 1, the pump 100 includes a drive shaft 116 extending from the upper end of the housing 102. The housing 102 defines a central axis 118 and an outer diameter xe2x80x98A.xe2x80x99 The drive shaft 116 is offset from the central axis 118 by a distance xe2x80x98B.xe2x80x99 This offset xe2x80x98Bxe2x80x99 creates several problems in aligning and connecting the drive shaft 116 of the pump 100 to the output shaft 120 of a motor 122 providing rotational force to the drive shaft 116. As shown in FIG. 3, the center of the cavity 108 is coincident with the central axis 118 of the pump 100, as the pump 100 is screwed into and seated in the cavity 108. The offset xe2x80x98Bxe2x80x99 of the drive shaft 116 from the central axis 118 results in the center of the drive shaft 116 orbiting in a circular path 124, having a radius equal to the offset xe2x80x98B,xe2x80x99 about the center 118 of the cavity 108, as the pump 100 is screwed into the cavity 108.
Slight dimensional differences in the configurations of the pump 100 and cavity 108, due to inherent manufacturing tolerances and variations in installation torques, result in the drive shaft 116 coming to rest at different positions along the circular path 124, when the seals 112, 114 are fully seated against the surfaces of the cavity 108. Because the position of the drive shaft 116 varies along the circular path 124, the motor 122 must be capable of mounting to the block 110 in any position wherein the drive shaft 116 might come to rest along the circular path 124, so that the output shaft 120 of the motor 122 may be properly aligned to engage the drive shaft 116 of the pump 100. This requires that the motor 122 be mounted to the block 110 with adjustable mounts, such as the pair of clamps 126, so that the output shaft 120 of the motor 122 may follow the drive shaft around the circular path 124 at the radius xe2x80x98B.xe2x80x99
As a result, even though the motor 122 has a diameter xe2x80x98C,xe2x80x99 the block 110 must be large enough to accommodate a motor footprint 128 having a diameter xe2x80x98Dxe2x80x99 equal to the diameter xe2x80x98Cxe2x80x99 of the motor 122 plus twice the offset xe2x80x98B.xe2x80x99 To accommodate the mounting clamps 126, the footprint may have to be even bigger, resulting in a valve block 110 having a minimum square or circular profile defining a dimension xe2x80x98E,xe2x80x99 as shown in FIGS. 3 and 4, that is much larger than the diameters of either the pump 100 or the motor 122. Much of the advantage of small size provided by the pressure clamped pump 100 is thus lost due to the offset xe2x80x98B.xe2x80x99
The offset xe2x80x98Bxe2x80x99 also creates other problems. There is no positive means of aligning the output shaft 120 of the motor 122 with the drive shaft 116 of the pump 100. If these shafts are not properly aligned, the misalignment places high stresses on the shafts 120, 116 which may cause the pump 100 and or motor 122 to fail prematurely. In addition, it is not possible to utilize provisions, such as the bolts 130 holding the motor 122 together, to also mount the motor 122 on the block 110, thereby precluding further reduction in size and complexity of the hydraulic apparatus.
As shown in FIG. 1, a pump 100 according to the ""715 patent utilizes a series of balls 132 for axially supporting the drive shaft 116 and an idler shaft 134 in the housing 102. Because the drive shaft 116 extends out of the upper end of the housing 102, the drive shaft 116 is supported only on its lower end by one of the balls 132. The drive shaft 116 is keyed to a drive gear 136 of the pump 100, and passes through a shaft seal 138 at the point of exit from the housing 102. Because the drive shaft 116 is supported axially only at the lower end by the ball 132, the drive shaft 116 of prior pressure clamped pumps may be inadvertently pulled out of the drive gear 136 and through the seal 138, thereby rendering the pump inoperative. This may occur, for example, during removal of the drive motor 122, if the motor output shaft 120 has become stuck together with the pump drive shaft 116 during operation, or if the motor 122 is not pulled straight off of the drive shaft 116 along the central axis 118, such that the output shaft 120 becomes canted with respect to the pump drive shaft 116 in a manner that would cause the drive shaft 116 to become wedged together with the output shaft 120 due to the canting of the motor 122.
The lower balls 132 also present an undesirable physical restriction upon the size, shape, and placement of the pump inlet 140, and present difficulties in manufacturing and assembling the pump 100.
My invention provides an improved hydraulic apparatus and pressure clamped pump that solves one or more of the problems described above through the use of pump having a housing adapted for installation into a cavity and a drive shaft coincident with the center of the housing. In some forms of my invention, the hydraulic apparatus includes piloting features for facilitating alignment of the pump drive shaft with the output shaft of a motor used to drive the pump. The pump may include elements for retaining the drive shaft within the pump, and may also include a larger and less restricted inlet than could be achieved in prior pressure clamped pumps.
In one form of my invention, a hydraulic apparatus includes a block having a cavity adapted for receiving a pressure clamped hydraulic pump. The pump has a central axis and a drive shaft extending along the central axis. The block further includes an inlet channel and an outlet channel, with the inlet channel being adapted for communicating with the cavity and an inlet of the pump, and the outlet channel adapted for communicating with the cavity and an outlet of the pump.
The pump of the hydraulic apparatus may include a housing defining a central axis, an inlet and an outlet. The pump may further include a plurality of pump components positioned in axially disposed relation to one another, and pumping means located in the housing for drawing fluid into the inlet at a first pressure and pumping the fluid from the outlet at a second pressure greater than the first pressure. The pump drive shaft extends from the housing along the central axis and is operatively connected to the pumping means, for drawing fluid into the inlet at a first pressure and pumping the fluid from the outlet at a second pressure greater than the first pressure, when the drive shaft is rotated about the central axis. The housing has a first internal axial area upon which the second pressure acts and a second external axial area greater than the first axial area. The pump inlet and the inlet channel are sealed from the pump outlet and the outlet channel such that the second pressure acts upon the second axial area when the pump is operated and applies a clamping force to the housing components.
The pumping means may be a gear pump having a single primary gear driving a single secondary gear. The pumping means may alternatively be a gear pump having a single primary gear driving two or more secondary gears. Where the pumping means includes two or more secondary gears, the drive shaft may be coincident with the center of the housing. The primary gear may also have a prime number of teeth to reduce wear.